1. Field of the Invention
The present invention relates generally to a heat exchanger for an automotive vehicle. More particularly, the present invention relates to an automotive heat exchanger core having a thermal stress-relieving zone therein.
2. Disclosure Information
Typical automotive heat exchangers, such as radiators, include a plurality of thin-walled tubes interleaved with corrugated fins enclosed in a core frame. The fins are rigidly attached to the tubes as well as to a pair of frame side supports while the tubes are joined to a pair of headers. The frame side supports are attached also to the headers. As is well known in the art, coolant passes from one header through the tubing to the other header. As the temperature of the coolant passing through the heat exchanger core increases, the core expands. The frame side supports, however, are not in direct heat contact with the liquid and, as such, do not heat at a proportional rate to the heating of the tubing. As a result of the expansion and contraction of the tubing, the side supports induce thermal stress in the tube-to-header joints during the thermal cycling of the heat exchanger, often leading to durability problems such as cracking or leaking of the tubes.
To overcome this thermal cycling problem and to increase the durability of the heat exchanger core, it is known in the art to relieve the thermally-induced stress by saw cutting the side supports following brazing of the core and prior to placing the heat exchanger core into service. However, the saw cutting operation is difficult to automate, is excessively loud, and produces a tremendous amount of metal fines resulting in increased downtime and increased maintenance of the saw.
Other methods have been proposed to relieve the thermally-induced stress in the heat exchanger core without the need for saw cutting the side supports. For example, U.S. Pat. No. 4,719,967 proposes the use of a "T-shaped" or "I-shaped" slot or piercing stamped into the core reinforcement prior to forming the reinforcement into a channel member. After brazing the core assembly, the reinforcement is fractured at the perforation to allow for expansion of the core during thermal cycling of the heat exchanger. The use of such a "T-shaped" or "I-shaped" perforation may be difficult to maintain since the perforation may fill up with filler metal such as cladding or solder during the brazing of the core and may also prematurely fracture upon bending the reinforcement into its channel shape. Furthermore, U.S. Pat. No. 4,719,967 does not suggest any apparatus for performing the fracturing of the core reinforcement. Therefore, it would be advantageous to provide a simpler and less complex perforation design to avoid these problems.
It is an object of the present invention to provide a heat exchanger having a core including a side support defining a thermal stress-relieving zone therein which maintains core rigidity during assembly and brazing of the heat exchanger core while offering an efficient and simple means to relieve thermally-induced stress experienced by the heat exchanger.
It is further an object of the present invention to provide a thermal stress-relieving zone which does not become occluded with brazing materials during the manufacture of the heat exchanger core.
There is disclosed herein a method of producing an automotive heat exchanger having thermal stress-relieving zone therein comprising the steps of assembling a heat exchanger core, the core having a frame including a pair of headers and a pair of side supports disposed between the headers. Each of the side supports includes a generally planar base portion and a pair of flanges extending generally perpendicularly to the plane of the base and including an elliptical aperture disposed in the base portion. The method further comprises the steps of supporting the assembled heat exchanger cores on conveying means for transporting the heat exchanger cores to a work station; securing the heat exchanger against movement at the work station; engaging at least one of the side supports proximate the elliptical aperture with tool means for shearing the flanges of the side support; and actuating the tool means to provide a shearing force against the flanges of the side support until the flanges are completely fractured to produce the thermal stress-relieving zone.
These and other objects, features and advantages of the present invention will be readily apparent from the drawings, detailed description and claims which follow.